Mixer circuit and RF transmitter using such mixer circuit

1. A mixer circuit comprising a mixer core for mixing an input frequency signal with a local oscillator signal, the input frequency signal comprising one or more input intermediate frequency signals:

a variable current block arranged to feed the mixer core with an amplified input signal, said variable current block arranged between an input for receiving the input frequency signal and the mixer core, said variable current block comprising transistors and switches to enable provision of a variable current; and

a voltage-to-current conversion block comprising transistors for performing a voltage-to-current conversion, said voltage to current conversion block receiving the one or more input intermediate frequency signals, converting a difference in a voltage of said one or more input intermediate frequency signals to a difference in current and outputting to said variable current block the corresponding difference in current,

wherein the local oscillator signal comprises a modulated signal generated by a digital phase locked loop circuit and modulated by phase information.

2. A mixer circuit comprising a mixer core for mixing an input frequency signal with a local oscillator signal, the mixer circuit comprising:

a variable current block arranged to feed the mixer core with an amplified input signal, said variable current block arranged between an input for receiving the input frequency signal and the mixer core, said variable current block comprising transistors and switches to enable provision of a variable current,

wherein said voltage to current conversion block further comprises a variable resistor (R v ) arranged between said transistors, for fine-tuning said variable current.

3. The mixer circuit as claimed in claim 2 , wherein said fine-tuning is performed in 1 dB steps.

4. The mixer circuit as claimed in claim 2 , wherein said voltage to current conversion block comprises a fixed resistor arranged between said transistors.

5. The mixer circuit as claimed in claim 4 , wherein the mixer circuit further comprises biasing transistor blocks generating bias currents to said variable current block, to said mixer core and to said voltage to current conversion block.

6. The mixer circuit as claimed in claim 5 , wherein the voltage to current conversion block and the biasing transistor blocks and the variable current block and the mixer core, respectively, are arranged to be fed individually.

7. A mixer circuit comprising:

a mixer core for mixing an input frequency signal with a local oscillator signal;

a variable current block arranged to feed the mixer core with an amplified input signal, said variable current block arranged between an input for receiving the input frequency signal and the mixer core, said variable current block comprising transistors and switches to enable provision of a variable current,

wherein a respective one of the transistors of said variable current block are connected, via a source/drain terminal thereof, in series with a respective one of said switches.

8. A radio frequency transmitter comprising a mixer circuit having a mixer core for mixing an input frequency signal with a local oscillator signal, the mixer circuit comprising:

a variable current block arranged to feed the mixer core with an amplified input signal, said variable current block arranged between an input for receiving the input frequency signal and the mixer core, and comprising transistors and switches for enabling provision of a variable current,

wherein the mixer circuit further comprises a voltage to current conversion block comprising transistors for performing a voltage to current conversion, and

wherein said voltage to current conversion block further comprises a variable resistor (R v ) arranged between said transistors, for fine tuning said variable current.

9. A radio frequency transmitter comprising a mixer circuit having a mixer core for mixing an input frequency signal with a local oscillator signal, the mixer circuit comprising:

a variable current block arranged to feed the mixer core with an amplified input signal, said variable current block arranged between an input for receiving the input frequency signal and the mixer core, and comprising transistors and switches for enabling provision of a variable current,

wherein signal output from said mixer circuit is fed directly to an antenna, a signal path between said mixer circuit and the antenna including no amplifiers.

10. A radio frequency transmitter comprising a mixer circuit having a mixer core for mixing an input frequency signal with a local oscillator signal, the mixer circuit comprising:

a variable current block arranged to feed the mixer core with an amplified input signal, said variable current block arranged between an input for receiving the input frequency signal and the mixer core, and comprising transistors and switches for enabling provision of a variable current,

wherein the mixer circuit further comprises a voltage to current conversion block comprising transistors for performing a voltage to current conversion, and

wherein said voltage to current conversion block comprises a fixed resistor arranged between said transistors.

11. The transmitter as claimed in claim 10 , wherein the mixer circuit further comprises biasing transistor blocks generating bias currents to said variable current block, said mixer core and said voltage to current conversion block.

12. The transmitter as claimed in claim 11 , wherein the voltage to current conversion block and the biasing transistor blocks and the variable current block and the mixer core, respectively, are arranged to be fed individually.

13. The transmitter as claimed in claim 8 , wherein a respective one of the transistors of said variable current block are connected in series with a respective one of said switches.

14. A mixer circuit comprising a mixer core for mixing an input frequency signal with a local oscillator signal, the input frequency signal comprising one or more input intermediate frequency signals:

a variable current block arranged to feed the mixer core with an amplified input signal, said variable current block arranged between an input for receiving the input frequency signal and the mixer core, said variable current block comprising transistors and switches to enable provision of a variable current,

wherein the local oscillator signal comprises a modulated signal generated by a digital phase locked loop circuit and modulated by phase information.